Selected Item in bookmarks. How would that work ?

Hello, 
I am quite confused on what the "Selected" configuration means in ookmark Navigators

I have 2 sets of bookmark navigators one on the left and a second level on top of my page.

However, navigating the horizontal level 2 bookmarks, makes it totally random the one selected on the left

Before you ask, it's never the same value selected, and I wen to the process of "updating" all my bookmarks with all the left and top blookmaked "looking selected" for evey bookmark of the app.

Thx for your help, 

Ps : An alternative would be to have page navigators where you could somehow build page hierachies and have secondary titles (as the technical name of the page might not be the one you want to display)